Cardiac function and long-term volume load : Physiological investigations in endurance athletes and in patients operated on for aortic regurgitation

Abstract: Background and aims. The heart is a remarkably adaptable organ, continuously changing its output to match metabolic demands and haemodynamic load. But also in long-term settings, such as in chronic or repeated volume load, there are changes in cardiac dimensions and mass termed cardiac hypertrophy. Depending on the stimulus imposing the volume load this hypertrophy differs in extent and phenotype. We aimed to study cardiac function in two settings with long-term volume load, including patients previously operated for aortic regurgitation and healthy females performing endurance training.Methods. In paper I, 21 patients (age 52±12 years, all male) operated on with aortic valve replacement for aortic regurgitation (AR) underwent a cardiopulmonary exercise test (CPET) and an echocardiographic evaluation in average 49±15 months following surgery. The peak oxygen uptake (peakVO2) was compared to results from a pre-operative and a six months follow-up, and relations to echocardiographic measures were determined.In papers II–IV, 48 endurance trained female athletes (ATH, age 21±2 years) were compared to 46 untrained females (CON, age 21±2 years) regarding echocardiographic measures of cardiac dimensions, global and regional cardiac function and maximal aerobic capacity (VO2max) determined with CPET. Relations between VO2max and cardiac variables were explored.Results. In paper I, peakVO2 had decreased from 26±6 to 23±5 mL/kg/min in patients from the first to second, late follow-up. This decrease was larger than expected by their increased age alone, and a majority of patients had a cardiorespiratory fitness below average according to reference values from healthy subjects of the same age, sex and weight.In papers II–IV, we found that ATH (VO2max 52±5 mL/kg/min) had larger atrial, ventricular and inferior vena cava dimensions compared to CON (VO2max 39±5 mL/kg/min). ATH had increased measures of right ventricular (RV) systolic function (RV atrioventricular plane displacement indexed by cardiac length 2.5±0.3 vs. 2.3±0.3, p=0.001) and left ventricular (LV) diastolic function (mitral E-wave velocity 0.92±0.17 vs. 0.86±0.11 m/s, p=0.029). In addition, systolic synchrony was similar between groups while there were heterogeneous differences in diastolic and systolic function across different myocardial segments. VO2max was most strongly related to LV end-diastolic volume (r=0.709, p<0.001).Conclusions. Decreasing peakVO2 following surgery for AR, despite a normalisation in cardiac dimension could either be a result of a remaining, slight myocardial dysfunction or post-operative negative influence on cardiac performance by filling disturbances or the prosthetic valve itself, or, a sign of an inadequate post-operative level of physical activity and lack of exercise training. This stresses the importance of post-operative management and methods for increasing aerobic capacity, where exercise testing could be valuable for guiding patients and tailoring exercise protocols.The eccentric cardiac hypertrophy in ATH, symmetrically distributed across the heart, depicts the physiological hypertrophy in response to volume load in endurance training. Cardiac function was similar, or for some measures slightly improved in ATH compared to CON and LV dimensions, rather than cardiac function, were predictors of VO2max. As the heart of female athletes has been far less studied than that in males, our results add knowledge regarding the female athlete’s heart, and our results of differences in segmental cardiac function merits further research.